Carbon-hydrogen and carbon-heteroatom bond activation using iridium(I) complexes

In this research, the B3LYP density functional and Stevens effective core potentials are used to compare carbon-hydrogen and carbon-heteroatom bond activation by an iridium(I) complex. Of particular importance is to address the kinetic (transition state) and thermodynamic (ground state) selectivity. The complex Ir(PH₃)₂(H) with CH₃-X (X=F, Cl, OH, SH, NH₂, PH₂) as the substrate has been used as a model. Good agreement in geometries is obtained between the target molecules and experimental models. The resultant products of C-H and C-X oxidative addition are Y-shaped minima (i.e., a distorted trigonal bipyramid with one acute and two obtuse angles among the equatorial ligands). Oxidative addition of the C-X bond to the substrate is exothermic for groups 16 and 17, but endothermic for group 15. A significant thermodynamic preference for C-X activation over C-H activation is observed for these Ir(I) complexes. However, analysis of the transition states for oxidative addition suggests that there is a kinetic preference for C-H activation.